WS_GROUP, any secret protocol between dialogbox-manager-WndProc and standard control?

Question

I'm reading Charles Petzold Programming Windows 5th-ed, Chapter 11, "Tabs Stops and Groups" section. I have a big question now.

The book says, when some controls belong to the same group, you can use left/right arrow key to switch focus between them, and this feature is used most often with a group of radio boxes. But what about other type of controls?

I tried having 3 button controls grouped together(A,B,C, only A has WS_GROUP, B and C don't). Then, I can confirm left/right arrow can switch focus between A,B and C.

Observing it more carefully, I see difference between radio box and button [P1]:

For a radio box group, pressing left/right-arrow repeatedly will cycle focus among all radio boxes in that group.
For button group, pressing right-arrow repeatedly will have focus move and stop at button C, the same left-arrow has it stop at A, no cycle behavior.

The case for "edit" control [P2]: If I make 3 edit boxes in one group, pressing left/right-arrow will NEVER switch the focus, which is not the same behavior as a button group.

So, my question boils down to: Does windows internal dialog box mananger WndProc (just call it DefDlgProc) treats some type of controls specially(like "edit")? For example, if DefDlgProc finds that a WM_KEYDOWN message with VK_RIGHT is destined for a "edit" control, it will never take the focus-switch action but pass the message to "edit" control honestly.

Is that special treatment done in a hard-coded way or some generic, configurable way? I need to know it because, if I write my own custom editbox control, I need a way to have DefDlgProc treat arrow keys specially for my control, right?

Sample code: For the 3-edit experiment, I use .rc statement like this:

ABOUTBOX DIALOGEX 32, 32, 180, 100
STYLE DS_MODALFRAME | WS_POPUP
EXSTYLE WS_EX_STATICEDGE
FONT 8, "Tahoma"
BEGIN
    EDITTEXT        IDC_EDIT0,40,7,40,14, ES_AUTOHSCROLL| WS_GROUP ,WS_EX_CLIENTEDGE 
    EDITTEXT        IDC_EDIT1,90,7,40,14, ES_AUTOHSCROLL           ,WS_EX_CLIENTEDGE
    EDITTEXT        IDC_EDIT2,133,7,40,14,ES_AUTOHSCROLL

    CONTROL         "OOKK",IDOK,"EllipPush",WS_GROUP | WS_TABSTOP,7,63,166, 30
    ICON            "ABOUT3",IDC_STATIC,7,7,20,20
END

Doing my experiment on Windows 7.

Jonathan Potter Jonathan Potter · Accepted Answer · 2015-10-06T04:36:40

Your question doesn't quite make sense. You wouldn't expect pressing the left or right cursor key in an edit control to shift the focus to another control, because the edit control itself consumes that keypress in order to move the cursor around.

Internally the dialog manager uses GetNextDlgGroupItem() to shift the focus to the next or previous control in the group. This doesn't distinguish between control types - it only looks at the WS_GROUP style. However, the dialog manager only calls this function if the control itself doesn't consume the key, and this is determined by the control's response to the WM_GETDLGCODE message.

WS_GROUP, any secret protocol between dialogbox-manager-WndProc and standard control?

1 Answers